Apparatus and method for managing a random access channel in a mobile communication system

ABSTRACT

A random access channel (RACH) management method performed by a user equipment (UE) in a mobile communication system and an apparatus are provided. The method includes receiving, from a network, a signal indicative of a resolution of contention in a RACH procedure before a contention resolution timer expires; determining, if the received signal includes a contention resolution message including a unique identifier (ID) of the UE, that the RACH procedure has been successfully completed; receiving, from the network, after the successful completion of the RACH procedure, a UE information transmit request; and transmitting, to the network, in response to receipt of the UE information transmit request, a response message including first information indicating that the contention is detected in at least one preamble transmitted for the completed RACH procedure and indicating a number of the at least one preamble in which the contention is detected.

PRIORITY

This continuation application claims priority under 35 U.S.C. §120 toU.S. patent application Ser. No. 14/054,329 (now U.S. Pat. No. 9,380,601issued on Jun. 28, 2016), which was filed in the U.S. Patent andTrademark Office on Oct. 15, 2013 and claims priority under 35 U.S.C.§120 to U.S. patent application Ser. No. 12/770,237 (now U.S. Pat. No.8,620,367 issued on Dec. 31, 2013), which was filed in the U.S. Patentand Trademark Office on Apr. 29, 2010 and claims priority under 35U.S.C. §119(a) to a Korean Patent Application filed in the KoreanIntellectual Property Office on Apr. 29, 2009 and assigned Serial No.10-2009-0037880, the entire content of each of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a mobile communicationsystem, and more particularly, to an apparatus and method for managing aRandom Access CHannel (RACH) in a mobile communication system.

2. Description of the Related Art

Long Term Evolution (LTE), which is the next-generation mobilecommunication system of Universal Mobile Telecommunication Service(UMTS) or the third generation mobile communication system, provideshigh-speed packet services based on Orthogonal Frequency DivisionMultiplexing (OFDM).

FIG. 1 illustrates an LTE mobile communication system.

Referring to FIG. 1, the LTE system has been simplified in a 2-nodestructure including Evolved Node Bs (ENBs) 120, 122, 124, 126 and 128,and anchor nodes 130 and 132. A User Equipment (UE) 101 accesses anInternet Protocol (IP) network using the ENBs and the anchor nodes. TheENBs are connected to the UE 101 by radio channels, and manage theircells and control radio resources.

For example, an ENB generates control information necessary in thecell(s) as system information, broadcasts the system information,allocates radio resources to exchange data and/or control informationwith UEs, and decides and performs a handover by acquiring, from UEs,channel measurement information of the current cell and adjacent cells.The ENB includes control protocols such as a Radio Resource Control(RRC) associated with radio resource management.

However, a more efficient random access procedure would greatly benefitthe next-generation mobile communication system. In particular, thenext-generation mobile communication system is still lacking a schemethat efficiently allocates random access resources consideringcollisions or contentions between random access preambles, which aresimultaneously transmitted from multiple UEs.

SUMMARY OF THE INVENTION

Accordingly, the present invention is designed to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages as will be described below. An aspect of the presentinvention provides an apparatus and method for optimizing randomaccess-related system resources by a network in a mobile communicationsystem.

Another aspect of the present invention provides an apparatus and methodfor efficiently managing RACHs by a network in a mobile communicationsystem.

Another aspect of the present invention provides an apparatus and methodfor setting random access preambles and resources by a network on anoptimized basis in a mobile communication system.

Another aspect of the present invention provides an apparatus and methodfor setting/resetting random access resources considering RACH preamblecollisions by a network in a mobile communication system.

Another aspect of the present invention provides an apparatus and methodfor automatically adjusting random access resources to be allocatedconsidering RACH preamble collisions by a network in a mobilecommunication system.

Another aspect of the present invention provides an apparatus andmethod, wherein a network transmits, to UEs, random access parametersthat have been set considering RACH preamble collisions in a mobilecommunication system.

Another aspect of the present invention provides an apparatus andmethod, wherein UEs report RACH preamble collision count and timeinformation to a network in a mobile communication system.

Another aspect of the present invention provides an apparatus andmethod, wherein UEs receive, from a network, parameters that were setconsidering RACH preamble collisions in a mobile communication system.

According to an aspect of the present disclosure, a RACH managementmethod performed by a UE in a mobile communication system is provided.The method includes receiving, from a network, a signal indicative of aresolution of contention in a RACH procedure before a contentionresolution timer expires; determining, if the received signal includes acontention resolution message including a unique identifier (ID) of theUE, that the RACH procedure has been successfully completed; receiving,from the network, after the successful completion of the RACH procedure,a UE information transmit request; and transmitting, to the network, inresponse to receipt of the UE information transmit request, a responsemessage including first information indicating that the contention isdetected in at least one preamble transmitted for the completed RACHprocedure and indicating a number of the at least one preamble in whichthe contention is detected.

According to another aspect of the present disclosure, a method formanaging a RACH by a network in a mobile communication system isprovided. The method includes transmitting, to a UE, a signal indicativeof a resolution of contention in a RACH procedure of the UE, wherein thesignal includes a contention resolution message including a unique ID ofthe UE; transmitting, to the UE, after transmitting the signal to theUE, a UE information transmit request; and receiving, from the UE, inresponse to the UE information transmit request, a response messageincluding first information indicating that the contention is detectedin at least one preamble transmitted for the RACH procedure andindicating a number of the at least one preamble in which the contentionis detected.

According to another aspect of the present disclosure, a UE apparatususing a RACH in a mobile communication system is provided. The UEapparatus includes a receiver configured to receive, from a network, asignal indicative of a resolution of contention in a RACH procedurebefore a contention resolution timer expires, determine, if the receivedsignal includes a contention resolution message including a unique ID ofthe UE, that the RACH procedure has been successfully completed, andreceive, from the network, after the successful completion of the RACHprocedure, a UE information transmit request; and a transmitterconfigured to transmit, to the network, in response to receipt of the UEinformation transmit request, a response message including firstinformation indicating that the contention is detected in at least onepreamble transmitted for the completed RACH procedure and indicating anumber of the at least one preamble in which the contention is detected.

According to another aspect of the present disclosure, a networkapparatus for managing a random access channel (RACH) in a mobilecommunication system is provided. The network apparatus includes atransmitter configured to transmit, to a UE, a signal indicative of aresolution of contention in a RACH procedure of the UE and transmit, tothe UE, after transmitting the signal to the UE, a UE informationtransmit request, wherein the signal includes a contention resolutionmessage including a unique ID of the UE; and a receiver configured toreceive, from the UE, in response to the UE information transmitrequest, a response message including first information indicating thatthe contention is detected in at least one preamble transmitted for theRACH procedure and indicating a number of the at least one preamble inwhich the contention is detected.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the present invention will be more apparent from thefollowing description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a diagram illustrating a next-generation mobile communicationsystem;

FIG. 2 is a diagram illustrating a conventional network structure;

FIG. 3 is a signal flow diagram illustrating a conventional RACHprocedure;

FIGS. 4A and 4B are signal flow diagrams illustrating an automaticoptimization method for RACH-related system resources according to anembodiment of the present invention;

FIG. 5 is a flowchart illustrating an operation of a UE according to anembodiment of the present invention;

FIG. 6 is a block diagram of a UE according to an embodiment of thepresent invention;

FIG. 7 is a flowchart illustrating an operation of a network accordingto an embodiment of the present invention; and

FIG. 8 is a block diagram of a network apparatus according to anembodiment of the present invention.

Throughout the drawings, the same drawing reference numerals will beunderstood to refer to the same elements, features and structures.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Various embodiments of the present invention will now be described indetail with reference to the accompanying drawings. In the followingdescription, descriptions of well-known functions and constructions areomitted for clarity and conciseness. In addition, terms used herein aredefined based on functions in the present invention and may varyaccording to users, operator intentions or usual practices. Therefore,the definition of the terms should be made based on contents throughoutthe specification.

While the present invention will be described using, for example, a3^(rd) Generation Partnership Project (3GPP) Long Term Evolution (LTE)system that has evolved from the 3GPP system, the present invention isapplicable to all mobile communication systems to which ENB schedulingis applied, without any modification. In addition, the present inventionis applicable to communication systems to which a random accessprocedure is applied. Additionally, the present invention is applicableto systems supporting uplink services.

As will be described below, a mobile communication system according toan embodiment of the present invention automatically optimizes preamblesand system resources regarding Radom Access CHannels (RACH). Inparticular, a method for automatically optimizing numberOfRA-Preambles,sizeOfRA-PreamblesGroupA and/or parach-ConfigIndex among RACH-relatedsystem resources is provided.

The numberOfRA-Preambles indicates information about the number ofpreambles used for a contention-based RACH, and thesizeOfRA-PreamblesGroupA indicates information about the number ofpreambles belonging to a preamble group A among a number of preamblesused for the contention-based RACH. The number of preambles belonging toa preamble group B may be represented by numberOfRA-Preambles minussizeOfRA-PreamblesGroupA. The parach-ConfigIndex indicates the number ofRACH resources (times and frequencies) allocated for each radio frame.

In a mobile communication system according to an embodiment of thepresent invention, a network includes an ENB and a Self-OptimizedNetwork (SON) server. To automatically optimize the RACH parameters inthe network, a UE records the number of preamble collisions (or apreamble collision count) and each preamble collision's time until aRACH procedure is successfully performed or until the RACH procedurefails, and then reports them to the network after completion of the RACHprocedure or upon receipt of a request from the network.

FIG. 2 illustrates a conventional LTE system including a network serversupporting automatic optimization.

A Self-Optimized Network (SON) refers to a network that automaticallyoptimizes (or self-optimizes) system resources and related parameters ofa cell. That is, without the network test that an operator staffdirectly performs, the network automatically optimizes system resourcesand related parameters, needed for data transmission that it has beenreported from UEs, or based on the statistical figures obtained throughthe measurement by the network itself.

Referring to FIG. 2, a UE 201 and an ENB 211 exchange data and controlinformation through a radio interface. A SON server 221 may determinepolicies appropriate for the ENB 211 and system resources and relatedparameters of the cell by receiving a report on the statistical figuresfrom the ENB 211. Some system resources and related parameters mayundergo a self-optimization operation in the ENB 211 itself, with theSON server 221 excluded.

FIG. 3 illustrates a conventional RACH procedure in an LTE system.

Referring to FIG. 3, a UE 301 selects a preamble group, randomly selectsa preamble in the selected group, and transmits the preamble to the ENB303 through predefined RACH resources in step 311. The rule in which theUE 301 selects a preamble group may follow, for example, the 3GPPstandard TS36.321v8.4.0. Generally, the UE 301 selects a preamble groupdepending on the current channel state and the size of a message to betransmitted.

The ENB 303, which has received the preamble in step 311, transmitsreceived preamble's ID information, Timing Advanced (TA) information foradjusting uplink timing, uplink resource allocation information formessage transmission by the UE 301, temporary UE ID information (orTemporary-Radio Network Temporary Identifier T-RNTI), etc., in step 321.

During uplink resource allocation, the ENB 303 may allocate differentuplink resources for each group depending on the preamble group to whichthe preamble received in step 311 belongs. For example, supposing that a‘messageSizeGroupA’ value, or a related parameter, is now b56, and isbeing broadcast through system information, if the received preamblebelongs to a preamble group A, uplink resources sufficient fortransmitting 56 bits are allocated. However, if the received preamblebelongs to a preamble group B, uplink resources sufficient fortransmitting more than 56-bit information may be allocated.

Upon receiving the uplink resource allocation information in step 321,the UE 301 determines whether or not the preamble transmitted in step311 corresponds with the preamble ID received in step 321, and if itdoes correspond, transmits a Layer 2 (L2)/Layer 3 (L3) message using theuplink resources allocated in step 321, in step 331.

If multiple UEs have used the same preamble in step 311, a collision ora contention may occur. In order to clearly indicate the UE,transmission data from which the ENB 303 has received, the ENB 303 thentransmits a UE's unique ID information (or Serving Temporary MobileSubscriber Identity (S-TMSI)) received in step 331 or a contentionresolution message with random ID information in step 341.

Therefore, multiple UEs that used the same preamble in step 311, receivethe contention resolution message in step 341, and check if the UE'sunique ID information or random ID information included in the messagereceived in step 341 corresponds to the values transmitted in step 331.If corresponding, the UEs continue to a next procedure. However, if theUE's unique ID information or random ID information included in themessage received in step 341 is different from the values the UEstransmitted in step 331, the UEs resume the RACH procedure.

Media Access Control (MAC) system parameters that the LTE systembroadcasts regarding RACH are defined in Table 1 as follows. For moredetails on these parameters, reference can be made to the 3GPP standardsTS36.331v8.4.0 and TS36.321v8.4.0.

TABLE 1 RACH-ConfigCommon preambleInfo > numberOfRA-Preambles ENUM {n4,n8, n12, n16, n20, n24, n28, n32, n36, n40, n44, n48, n52, n56, n60,n64} > preamblesGroupAConfig >> sizeOfRA-PreamblesGroupA ENUM {n4, n8,n12, n16, n20, n24, n28, n32, n36, n40, n44, n48, n52, n56, n60,spare1} >> messageSizeGroupA ENUM {b56, b144, b208, spare1} >>messagePowerOffsetGroupB ENUM {minusinfinity, spare1}powerRampingParameters > powerRampingStep ENUM {dB0, dB2, dB4, dB6} >ENUM {dBm-120, dBm-118, dBm-116, dBm-114, dBm-preambleInitialReceivedTargetPower 112, dBm-110, dBm-108, dBm-106,dBm-104, dBm- 102, dBm-100, dBm-98, dBm-96, dBm-94, dBm-92, dBm-90}ra-SupervisionInfo > preambleTransMax ENUM {n3, n4, n5, n6, n7, n8, n10,n20, n50, n100, n200, spare5, spare4, spare3, spare2, spare1} >ra-ResponseWindowSize ENUM {sf2, sf3, sf4, sf5, sf6, sf7, sf8, sf10} >mac-ContentionResolutionTimer ENUM {sf8, sf16, sf24, sf32, sf40, sf48,sf56, sf64} maxHARQ-Msg3Tx INT (1..8)

PHYsical (PHY) system parameters that the LTE system broadcastsregarding RACH are defined in Table 2 as follows. For more details onthese parameters, reference can be made to the 3GPP standards TS36.331and TS36.211.

TABLE 2 PRACH-ConfigSIB rootSequenceIndex INT (0 . . . 837)prach-ConfigInfo > prach-ConfigIndex INT (0 . . . 63) > highSpeedFlagBOOLEAN > zeroCorrelationZoneConfig ENUM {0 . . . 15) > prach-FreqOffsetINT (0 . . . 94)

Although, in FIG. 3, the UE 301 is notified in step 321 of the preambleID indicating the preamble it selected/transmitted in step 311 (thescheduling information for step 321 is transmitted through a PhysicalDownlink Common Control Channel (PDCCH) specific to Random Access RadioNetwork Temporary Id (RA-RNTI) (UE's unique ID information for randomaccess) mapped to the RACH resource the UE used in step 311), if the UEfails to receive UE's unique ID information (S-TMSI) or random numberinformation it transmitted in step 331 through the message of step 341before a preamble contention resolution timer expires (the preamblecontention resolution timer starts if the message of step 331 istransmitted), or if the UE is an RRC-connected UE and fails to receiveUE-specific scheduling information through a PDCCH specific to a CellRadio Network Temporary Identifier (C-RNTI) the UE uses, then the UE,regarding this as a preamble collision, increases the preamble collisioncount by 1 every time the preamble collision occurs, and records a timeof each preamble collision, until successful RACH is completed or untilthe UE senses a RACH failure.

The preamble collision count and the time information of each preamblecollision are reported to the network along with a cell ID with whichthe RACH has been performed, after completion of successful RACH or uponreceipt of a request from the network.

Upon receiving the above information from the UE, the network calculatesa preamble collision probability statistic value using a ratio of thepreamble collision count to the number of received preambles for aparticular time, and allocates the number of preambles and the number ofRACH resources to be used for the contention-based RACH by matching thepreamble collision probability statistic value to a target preamblecollision probability value.

For example, if the preamble collision probability statistic valuecalculated based on the ratio of the preamble collision count to thenumber of received preambles for a particular time is now 5%, the numberof preambles or the number of RACH resources to be used for thecontention-based RACH is increased to maintain the preamble collisionprobability statistic value at the target preamble collision probabilityvalue (e.g., 1%). In the present invention, preambles in whichnumberOfRA-Preambles and sizeOfRA-PreamblesGroupA appear are alsoreferred to as preambles.

Regarding the automatic adjustment of the parameters in the network, theENB may perform the overall adjustment. Otherwise, the ENB may generatea statistic value by collecting information from UEs and report thegenerated statistic value to a SON server, and the SON server maydetermine parameter values and notify the ENB of the determinedparameter values.

FIGS. 4A and 4B illustrate a method for automatically optimizing thenumber of preambles and the number of RACH resources used forcontention-based RACH, according to an embodiment of the presentinvention.

Referring to FIG. 4, when a RACH procedure is initially started, a UE401 stores a Cell Global ID (CGI) and initializes a preamble collisioncount to 0 in step 411. The UE 401 transmits a randomly selectedpreamble from a selected preamble group to an ENB 403 in step 413.

Upon receiving the preamble, the ENB 403 transmits preamble IDinformation ‘Preamble id’, uplink timing information ‘Timing Advanced(TA)’ uplink resource allocation information (UL Grant) for uplinkmessage transmission, etc., in step 415. The resource schedulinginformation for the transmission of step 415 is transmitted over aPhysical Downlink Control Channel (PDCCH) that uses an RA-RNTI that isspecific to RACH resources.

The UE 401 receives the scheduling information for step 415 over thePDCCH using the RACH resource-specific RA-RNTI, used in step 413,determines whether or not the Preamble id of step 415 indicates thepreamble transmitted in step 413, in step 421, and if so, transmits aninitial L2/L3 uplink message using the uplink resources allocated instep 415, in step 423.

The message transmitted in step 423 may include unique ID informationabout the UE 401 (UE S-TMSI) or a random number.

After the uplink message of step 423 is transmitted, the UE 401 starts apreamble contention resolution timer.

If the UE 401 fails to receive the unique ID information or randomnumber it transmitted in step 423, through a contention resolutionmessage in step 425 a, before the preamble contention resolution timerexpires, or if the UE 401 is an RRC-connected UE and fails to receivethe UE-specific scheduling information over the C-RNTI specific PDCCHthat the UE 401 is maintaining in step 425 b, then the UE 401 increasesthe preamble collision count by 1 and records time information of thepreamble collision in step 431, concluding that a preamble collision hasoccurred.

The time information of the preamble collision may be defined as one ofthe preamble transmission timing of step 413, the timing at which theRACH response message was received in step 415, the timing at which theUE 401 transmitted the initial L2/L3 uplink message in step 423, and thetiming at which the preamble contention resolution timer expires thatdetected the preamble collision. In accordance with an embodiment of thepresent invention, the preamble transmission timing of step 413 isassumed as the time of the preamble collision.

Until the RACH procedure is successfully completed or the RACH procedureis detected as ‘failure’, the UE 401 increases the preamble collisioncount every time the preamble collision occurs, and stores timeinformation of each preamble collision in step 441.

The ENB 403 may request UEs in the cell to transmit at least one of therecorded/stored CGI, the preamble collision count, and each preamblecollision's time information in step 451.

After receiving the request of the ENB 403 in step 451, the UE 401transmits at least one of the CGI, the preamble collision count, andeach preamble collision's time information stored in step 441, to theENB 403 in step 453.

In an alternative embodiment, the UE 401 may transmit the CGI, thepreamble collision count, and each preamble collision's time informationstored in step 441 to the ENB 403, upon successful completion of theRACH procedure, without a separate request of the ENB 403. In this case,the message in step 451 is not necessary.

The ENB 403 calculates preamble collision probability statistic valuesfor a particular time using the values received from UEs in step 461.The preamble collision probability statistic values for a particulartime are calculated using the number of preambles received for theparticular time and the number of preamble collisions that have occurredfor the particular time.

While (‘number of preamble collisions occurring for a particulartime’/‘number of preambles received for the particular time’)*100 isdescribed by way of example herein, any other formulae using the numberof preambles received for the particular time and the number of preamblecollisions occurring for the particular time may also be used.

The ENB 403 reports the preamble collision probability statistic valuescreated in step 461 to a SON server 405 in step 473. This report may bemade in response to a separate request that is received from the SONserver 405 in step 471.

Upon receiving the preamble collision probability statistic value instep 473, the SON server 405 calculates the number of preambles and thenumber of RACH resources to match the preamble collision probabilitystatistic value to a target preamble collision probability value (e.g.,1%), and resets the above-stated related parametersnumberOfRA-Preambles, sizeOfRA-PreamblesGroupA, and parach-ConfigIndexin step 481.

If the received preamble collision probability statistic value isgreater than the target preamble collision probability value, forexample, if the preamble collision probability statistic value is 5% andthe target preamble collision probability value is 1%, then the numberof preambles or the number of RACH resources is increased to match thepreamble collision probability statistic value to the target preamblecollision probability value. However, if the received preamble collisionprobability statistic value is less than the target preamble collisionprobability value, for example, if the preamble collision probabilitystatistic value is 0.1% and the target preamble collision probabilityvalue is 1%, then the number of preambles or the number of RACHresources is reduced to match the preamble collision probabilitystatistic value to the target preamble collision probability value.

In step 483, the SON server 405 notifies the ENB 403 of the parametersnumberOfRA-Preambles, sizeOfRA-PreamblesGroupA, and parach-ConfigIndexthat were set/reset in step 481. The ENB 403 resets the related RACHparameters to the values notified by the SON server 405 in step 491, andnotifies the reset parameters to UEs in the cell, including the UE 401,as system information, in step 493.

Although FIG. 4 illustrates that the ENB 403 generates statistic valuesby collecting information from UEs 401 and reports the generatedstatistic values to the SON server 405, and the SON server 405determines parameters based on the statistic values and notifies the ENB403 of the determined parameters, according to an embodiment of thepresent invention, the automatic adjustment operations for theparameters may also be performed in the ENB 403.

FIG. 5 illustrates an operation of a UE according to an embodiment ofthe present invention.

Referring to FIG. 5, a RACH procedure starts in step 501. In step 511,the UE stores a CGI of a cell wherein the RACH procedure is beingperformed, and initializes a preamble collision count to 0.

In step 521, the UE selects and transmits (or reselects and transmits) apreamble. If the UE receives scheduling information over an RA-RNTIspecific PDCCH mapped to the RACH resources used in step 521 andreceives a RACH response message (or a Random Access Response (RAR))including a Preamble Id indicating the preamble transmitted in step 521,over DownLink (DL) resources indicated by the scheduling information(YES in step 531), then the UE transmits an initial L2/L3 message usingUpLink (UL) resources (e.g., a UL Grant) included in the RACH responsemessage in step 541.

The initial L2/L3 message includes the UE's unique ID (UE S-TMSI) orrandom number information, and upon transmitting the initial L2/L3message, the UE starts a preamble contention resolution timer in step541. If the Preamble Id does not indicate the preamble transmitted instep 521, in step 531 (NO in step 531), the UE performs preamblereselection and retransmission in step 521.

If the UE fails to receive a RACH contention resolution messageincluding the UE's unique ID or random number information transmitted instep 541 (NO in step 553), before the preamble contention resolutiontimer expires in step 551, or if the UE is an RRC-connected UE and failsto receive UE-specific scheduling information over a C-RNTI specificPDCCH in use by the RRC-connected UE (NO in step 555), when the preamblecontention resolution timer expires (YES in step 551), the UE increasesthe preamble collision count by 1 and stores time information of eachpreamble collision in step 561.

However, if the UE receives the RACH contention resolution messageincluding the UE's unique ID or random number information transmitted instep 541 (YES in step 553), before the preamble contention resolutiontimer expires in step 551, or if the UE is an RRC-connected UE andreceives the UE-specific scheduling information over the C-RNTI specificPDCCH in use by the RRC-connected UE (YES in step 555), the UE stops thepreamble contention resolution timer and regards it as a success in theRACH procedure in step 557.

If the RACH procedure is successfully completed or a RACH procedurefailure is detected (YES in step 571), the UE stores the CGI, thepreamble collision count and each preamble collision's time informationin step 581.

As to the CGI, preamble collision count and each preamble collision'stime information of step 581, the UE may transmit the above informationto the ENB and reset the information of step 581, after RACH completion(in Alternative #1), or the UE transmit may transmit the aboveinformation to the ENB and reset the information of step 581, uponreceipt of a request message from the ENB (in Alternative #2), in step591.

However, before the RACH procedure is successfully completed or the RACHprocedure failure is detected (NO in step 571), the UE performs thepreamble reselection and retransmission in step 521.

FIG. 6 is a block diagram of a UE according to an embodiment of thepresent invention.

Referring to FIG. 6, the UE includes a preamble selector 601 forselecting a preamble and transmitting it to an ENB by way of atransceiver 611.

A preamble collision detector 631 detects a preamble collision eventusing a preamble contention resolution timer 621 and the RACH contentionresolution message or PDCCH scheduling information received through thetransceiver 611.

If a preamble collision is detected in the preamble collision detector631, a preamble collision count and collision time information recorder641 increases a preamble collision count and records each preamblecollision's time for each CGI.

The information recorded in the preamble collision count and collisiontime information recorder 641 is transmitted to an ENB or a SON serverthrough the transceiver 611, and the information is reset if thetransmission is completed.

FIG. 7 illustrates an operation of a network node according to anembodiment of the present invention.

Referring to FIG. 7, the network receives preamble collision counts andeach preamble collision's time information from UEs for each CGI in step701.

In step 711, the network calculates a preamble collision probabilitystatistic value using a ratio of the number of preambles received for aparticular time to a number of preamble collisions that have occurredfor a particular time.

While (‘number of preamble collisions occurring for a particulartime’/‘number of preambles received for the particular time’)*100 isdescribed herein by way of example, as described above, other formulaeusing the number of preambles received for the particular time and thenumber of preamble collisions occurring for the particular time may alsobe used.

If the preamble collision probability statistic value calculated in step711 is greater than the target preamble collision probability value, forexample, if the preamble collision probability statistic value is 5% andthe target preamble collision probability value is 1% (YES in step 721),the network increases the number of RACH preambles or the number ofallocated RACH resources to match the preamble collision probabilitystatistic value to the target preamble collision probability value, andresets the related parameters numberOfRA-Preambles,sizeOfRA-PreamblesGroupA, and parach-ConfigIndex accordingly in step731.

However, if the preamble collision probability statistic valuecalculated in step 711 is less than the target preamble collisionprobability value, for example, if the preamble collision probabilitystatistic value is 0.1% and the target preamble collision probabilityvalue is 1% (NO in step 721), then the network reduces the number ofpreambles or the number of allocated RACH resources to match thepreamble collision probability statistic value to the target preamblecollision probability value, and resets the related parametersnumberOfRA-Preambles, sizeOfRA-PreamblesGroupA, and parach-ConfigIndexaccordingly in step 733.

The parameters readjusted in steps 731 and 733 are notified to apertinent ENB in step 741. Thus, the ENB resets the related systeminformation to the values received in step 741, and notifies the resetvalues to UEs in the cell as system information in step 751. While ithas been described that the network sets the parameters by way ofexample, alternatively, the ENB itself may automatically adjust orself-adjust the parameters.

Additionally, the operations illustrated FIG. 7 may be performed inindependent network nodes on a separated basis according to operatorpolicy. For example, steps 701 to 751, except for step 741, may beperformed in the ENB. While the operations of steps 721 to 741 may beperformed in the SON server, the operations of steps 701, 711, and 751may be performed in the ENB. In this case, a procedure is needed inwhich the ENB transmits the preamble collision probability statisticvalue calculated in step 711 to the SON server. Also, the operations ofsteps 701 to 741 may be performed in the SON server, and the operationof step 751 may be performed in the ENB.

The present invention does not preclude any of these options. Using thesignal flow illustrated in FIG. 4, the ENB 403 performs steps 701, 711,and 751, and performs step 711 to transmit the statistic value to theSON server 405. The SON server 405 performs steps 721 to 741.

FIG. 8 is a block diagram illustrating a network node according to anembodiment of the present invention.

Referring to FIG. 8, the network node includes a transceiver 801 forcommunicating with UEs and transmitting system information in the cell.

The information collected from UEs by the transceiver 801, in accordancewith an embodiment of the present invention, is stored in informationstorage 811, and based on this information, a preamble collisionprobability statistic value generator 821 calculates preamble collisionprobability statistic values for a particular time.

A target preamble collision probability comparison/analysis unit 831compares/analyzes the preamble collision probability statistic valuesfrom the preamble collision probability statistic value generator 821,with the target preamble collision probability value. A RACH parameterdeterminer 841 determines the number of preambles or the number ofallocated RACH resources to be used for contention-based RACH, based onthe results from the target preamble collision probabilitycomparison/analysis unit 831. The RACH parameter determiner 841 resetsthe related parameters numberOfRA-Preambles, sizeOfRA-PreamblesGroupA,and parach-ConfigIndex. The reset RACH parameters are notified to UEs inthe cell through the transceiver 801.

The operation of FIG. 8 may be performed in independent network nodes ona separated basis according to operator policy. For example, all of theoperations of the entities 801 to 841 may be performed in an ENB.

While operations of the target preamble collision probabilitycomparison/analysis unit 831 and the RACH parameter determiner 841 maybe performed in a SON server, operations of the transceiver 801, theinformation storage 811, and the preamble collision probabilitystatistic value generator 821 may be performed in the ENB. In this case,a separate block is used, in which the ENB transmits the preamblecollision probability statistic value calculated by the preamblecollision probability statistic value generator 821, to the SON server.

Additionally, operations of the entities the information storage 811,the preamble collision probability statistic value generator 821, thetarget preamble collision probability comparison/analysis unit 831, andthe RACH parameter determiner 841 may be performed in the SON server,and the operation of the transceiver 801 may be performed in the ENB.

As is apparent from the foregoing description, the various embodimentsof the present invention can efficiently allocate system resourcesregarding the random access procedure in the mobile communicationsystem, contributing to an increase in random access capacity.

In particular, RACH parameters are set considering RACH collisions,thereby providing a more accurate optimized random access procedure.

While the present invention has been shown and described with referenceto certain embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A random access channel (RACH) management methodperformed by a user equipment (UE) in a mobile communication system,comprising: receiving, from a network, a signal indicative of aresolution of contention in a RACH procedure before a contentionresolution timer expires; determining, if the received signal includes acontention resolution message including a unique identifier (ID) of theUE, that the RACH procedure has been successfully completed; receiving,from the network, after the successful completion of the RACH procedure,a UE information transmit request; and transmitting, to the network, inresponse to receipt of the UE information transmit request, a responsemessage including first information indicating that the contention isdetected in at least one preamble transmitted for the completed RACHprocedure and indicating a number of the at least one preamble in whichthe contention is detected.
 2. The method of claim 1, furthercomprising: receiving, from the network, a notification including atleast one reset parameter that is related to at least one of a number ofRACH preambles and a number of RACH resources.
 3. The method of claim 2,wherein the at least one reset parameter is reset based on thecontention information.
 4. The method of claim 2, wherein the at leastone reset parameter includes a ‘numberOfRA-Preambles’ parameter, a‘sizeOfRA-PreamblesGroupA’ parameter, and a ‘prach-ConfigIndex’parameter.
 5. The method of claim 1, further comprising: storing, beforedetermining that the contention in the RACH procedure is resolved byreceiving the signal, the contention information when the contention inthe RACH procedure occurs.
 6. The method of claim 1, wherein theresponse message includes time information of the at least one preamblein which the contention is detected.
 7. A method for managing a randomaccess channel (RACH) by a network in a mobile communication system,comprising: transmitting, to a user equipment (UE), a signal indicativeof a resolution of contention in a RACH procedure of the UE, wherein thesignal includes a contention resolution message including a uniqueidentifier (ID) of the UE; transmitting, to the UE, after transmittingthe signal to the UE, a UE information transmit request; and receiving,from the UE, in response to the UE information transmit request, aresponse message including first information indicating that thecontention is detected in at least one preamble transmitted for the RACHprocedure and indicating a number of the at least one preamble in whichthe contention is detected.
 8. The method of claim 7, furthercomprising: resetting at least one parameter that is related to at leastone of a number of RACH preambles and a number of RACH resources; andtransmitting a notification including the at least one parameter.
 9. Themethod of claim 8, wherein the at least one parameter is reset based onthe contention information.
 10. The method of claim 8, wherein the atleast one parameter includes a ‘numberOfRA-Preambles’ parameter, a‘sizeOfRA-PreamblesGroupA’ parameter, and a ‘prach-ConfigIndex’parameter.
 11. The method of claim 7, wherein the response messageincludes time information of the at least one preamble in which thecontention is detected.
 12. A user equipment (UE) apparatus using arandom access channel (RACH) in a mobile communication system,comprising: a receiver configured to receive, from a network, a signalindicative of a resolution of contention in a RACH procedure before acontention resolution timer expires, determine, if the received signalincludes a contention resolution message including a unique identifier(ID) of the UE, that the RACH procedure has been successfully completed,and receive, from the network, after the successful completion of theRACH procedure, a UE information transmit request; and a transmitterconfigured to transmit, to the network, in response to receipt of the UEinformation transmit request, a response message including firstinformation indicating that the contention is detected in at least onepreamble transmitted for the completed RACH procedure and indicating anumber of the at least one preamble in which the contention is detected.13. The UE apparatus of claim 12, wherein the receiver is furtherconfigured to: receive, from the network, a notification including atleast one reset parameter that is related to at least one of a number ofRACH preambles and a number of RACH resources.
 14. The UE apparatus ofclaim 13, wherein the at least one reset parameter is reset based on thecontention information.
 15. The UE apparatus of claim 13, wherein the atleast one reset parameter includes a ‘numberOfRA-Preambles’ parameter, a‘sizeOfRA-PreamblesGroupA’ parameter, and a ‘prach-ConfigIndex’parameter.
 16. The UE apparatus of claim 12, wherein the receiver isfurther configured to: store the contention information when thecontention in the RACH procedure occurs.
 17. The UE apparatus of claim12, wherein the response message includes time information of the atleast one preamble in which the contention is detected.
 18. A networkapparatus for managing a random access channel (RACH) in a mobilecommunication system, comprising: a transmitter configured to transmit,to a user equipment (UE), a signal indicative of a resolution ofcontention in a RACH procedure of the UE and transmit, to the UE, aftertransmitting the signal to the UE, a UE information transmit request,wherein the signal includes a contention resolution message including aunique identifier (ID) of the UE; and a receiver configured to receive,from the UE, in response to the UE information transmit request, aresponse message including first information indicating that thecontention is detected in at least one preamble transmitted for the RACHprocedure and indicating a number of the at least one preamble in whichthe contention is detected.
 19. The network apparatus of claim 18,further comprising: a controller configured to reset at least oneparameter that is related to at least one of a number of RACH preamblesand a number of RACH resources, and wherein the transmitter is furtherconfigured to transmit a notification including the at least oneparameter.
 20. The network apparatus of claim 19, wherein the at leastone parameter is reset based on the contention information.
 21. Thenetwork apparatus of claim 19, wherein the at least one parameterincludes a ‘numberOfRA-Preambles’ parameter, a‘sizeOfRA-PreamblesGroupA’ parameter, and a ‘prach-ConfigIndex’parameter.
 22. The network apparatus of claim 18, wherein the responsemessage includes time information of the at least one preamble in whichthe contention is detected.